1. Field of the Invention
The present relates to a radio receiver receiving an analog broadcast signal and a digital broadcast signal, both having the same broadcast contents, and carrying out a reproduction operation for these signals.
2. Description of the Related Art
Conventionally, there has been known a radio receiver which receives an analog broadcast signal and a digital broadcast signal contained in the same frequency band, and carrying out reproduction operations appropriate for the respective broadcast signals in parallel (for example, see PCT International Application No. 2001-520479). This radio receiver receives, for example, a main broadcast signal of digital modulated signals, and a redundant signal of an analog FM modulated signal whose contents are the same as those of the main broadcast signal delayed by a predetermined time, and the reproduction operation is carried out using the redundant signal if the main broadcast signals are damaged, or the main broadcast signals are not received. As a result, it is possible to properly reproduce a broadcast program even if the reception of the main broadcast signal is interrupted.
In the radio receiver disclosed in the above patent publication, the digital broadcast signals are arranged in side-bands of the analog FM broadcast signal, and thus, a wider frequency band is necessary compared with a case where only the analog FM broadcast signal is received. For example, while the frequency band is set to 150 kHz if only the analog FM broadcast signal is received, the frequency band is set to 500 kHz if both the analog FM broadcast signal and the digital broadcast signals are received.
In present analog FM broadcast in the United States, the receive frequencies are assigned at an interval of 200 kHz, and thus, if a broadcast station (adjacent station) transmitting a broadcast signal with a wide frequency band including an analog FM broadcast signal and digital broadcast signals exists at a frequency adjacent to a receive frequency (frequency within ±200 kHz of the receive frequency), the noise floor in the receive frequency increases due to the digital broadcast signals contained in the side-bands. An ordinary receiver includes an S meter for detecting a receive electric field strength of a broadcast signal, and carries out various types of control operations (such as high-cut processing, and soft mute processing) based on this detected signal, and thus, there is the problem that if the level of the signal detected by the S meter changes depending on the existence of an adjacent station broadcasting a signal including digital broadcast signals in side-bands, various types of control operations are not carried out normally, and consequently, a proper operation state cannot be attained.